1. Field of the Invention
The present invention relates to a fluid selection valve unit applied to an exhaust gas control valve, a waste gate valve, or the like which is provided between a high-pressure-stage supercharger and a low-pressure-stage supercharger of a two-stage supercharging exhaust turbocharger so as to control an amount of exhaust gas supplied to the low-pressure-stage supercharger.
2. Description of the Related Art
In recent years, a vehicle diesel engine adopts a two-stage supercharging exhaust turbocharger which includes a high-pressure-stage supercharger having a high-pressure turbine driven by exhaust gas discharged from an engine and a low-pressure-stage supercharger having a low-pressure turbine driven by the exhaust gas used to drive the high-pressure-stage supercharger, wherein the high-pressure-stage supercharger and the low-pressure-stage supercharger are arranged in series in an exhaust gas passageway, and wherein air subjected to a first-stage pressurizing operation of the low-pressure compressor of the low-pressure-stage supercharger is subjected to a second-stage pressurizing operation of the high-pressure compressor of the high-pressure-stage supercharger and is supplied to an engine.
In the engine provided with the multi-stage supercharging exhaust turbocharger, a two-stage supercharging operation using both the high-pressure-stage supercharger and the low-pressure-stage supercharger is carried out in a low-speed running region, which is advantageous in a transient characteristic and an increase of low-speed torque of the engine.
Additionally, a one-stage supercharging operation using the low-pressure-stage supercharger is carried out in a high-speed running region of the engine and upon increasing an output and a supercharging pressure of the engine by allowing the exhaust gas to bypass the high-pressure-stage supercharger. In this manner, it is possible to further improve efficiency of the compressor and thus to realize a reliable running state having an excellent degree of freedom in matching.
FIG. 4 is an explanatory view showing an operation of the two-stage supercharging exhaust turbocharger.
In FIG. 4, Reference Numeral 1 denotes a high-pressure-stage supercharger, where the high-pressure-stage supercharger 1 includes a high-pressure turbine 1a and a high-pressure compressor 1b coaxially driven by the high-pressure turbine 1a. Reference Numeral 2 denotes a low-pressure-stage supercharger, where the low-pressure-stage supercharger 2 includes a low-pressure turbine 2a and a low-pressure compressor 2b coaxially driven by the low-pressure turbine 2a. 
The exhaust gas discharged from a cylinder 100 of the engine is collected in an exhaust manifold 103 and is supplied to the high-pressure turbine 1a of the high-pressure-stage supercharger 1 via an exhaust pipe 4. A part of the exhaust gas is supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 via an exhaust gas control valve 5, an exhaust pipe 6, and an exhaust pipe 10.
Here, the exhaust gas control valve 5 shown in a Y part of FIG. 4 is provided between the high-pressure-stage supercharger 1 and the low-pressure-stage supercharger 2, and is used to control a relationship between an amount of the exhaust gas of the high-pressure-stage supercharger 1 and an amount of the exhaust gas bypassing the high-pressure-stage supercharger 1 and supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 by controlling an opening degree thereof. That is, the exhaust gas passing through the high-pressure turbine 1a of the high-pressure-stage supercharger 1 and an exhaust pipe 8 and the exhaust gas of which a flow rate is controlled by the exhaust gas control valve 5 are mixed at an exhaust pipe 9 and the mixed gas is supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 via an exhaust pipe 10.
In the low-pressure-stage supercharger 2, the low-pressure compressor 2b is coaxially driven by the low-pressure turbine 2a so as to pressurize air supplied from an air cooler 2c, and the pressurized air is supplied to the high-pressure compressor 1b of the high-pressure-stage supercharger 1 via an air supply pipe 21 and an air supply suction pipe 18.
In the high-pressure-stage supercharger 1, the high-pressure compressor 1b is coaxially driven by the high-pressure turbine 1a so as to supply the pressurized air to a cylinder 100 of an engine via an air supply pipe 20, an intercooler 21, an air supply pipe 22, and an exhaust manifold 101.
Here, a compressor bypass valve unit 05 is provided in a bypass pipe 17 of the high-pressure compressor 1b so as to control an amount of air bypassing the high-pressure compressor 1b. 
Additionally, a waste gate valve 12 is provided in a bypass pipe 11 of the low-pressure turbine 2a so as to control an amount of exhaust gas bypassing the low-pressure turbine 2a. 
Here, as described above, the exhaust gas control valve 5 controls an opening degree thereof so as to control a relationship between an amount of exhaust gas of the high-pressure-stage supercharger 1 and an amount of exhaust gas bypassing the high-pressure-stage supercharger 1 and supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2, and an example thereof is shown in FIG. 5.
In FIG. 5, the exhaust gas control valve 5 includes a valve member 054 and a valve seat 055 on which the valve member 054 is seated, where one end of the valve member 054 is supported to a rotary shaft 52 so as to be rotatable about a shaft center 52a of the rotary shaft 52 in a direction indicated by the arrow W in terms of a support arm 56.
The low surface 054a of the valve member 054 is formed into a plane. When the valve member 054 is swung about the shaft center 52a of the rotary shaft 52, a low surface 054a of the valve member 054 comes into contact with a lower surface 055a of the valve seat 055 to thereby close the valve member 054.
Upon opening the valve member 054, the rotary shaft 52 is rotated by an exhaust gas control valve driving unit (not shown) in a direction indicated by the arrow W shown in FIG. 5 so as to be away from the valve seat 055, thereby opening the valve member 054 in terms of the support arm 56.
Additionally, in Patent Document 1 (Japanese Patent Application Laid-Open No. S61-291725), an exhaust gas control valve 6 is provided between a high-pressure-stage supercharger 1 and a low-pressure-stage supercharger 2, and is used to control an opening degree thereof so as to control a relationship between an amount of exhaust gas of the high-pressure-stage supercharger 1 and an amount of exhaust gas bypassing the high-pressure-stage supercharger 1 and supplied to the low-pressure-stage supercharger 2.
FIG. 3A is a view showing a relationship between a passage area and an opening degree of the exhaust gas control valve, and FIG. 3B is a view showing a relationship between an engine rpm and an engine torque.
When the lower surface 054a of the parallel valve-type valve member 054 comes into contact with the lower surface 055a of the straight valve seat 055 as shown in FIG. 5, a passage area of the valve member 054 varies linearly with respect to the opening degree of the valve member as shown by the line B of FIG. 3A.
Meanwhile, in a variable two-stage region running state of the two-stage supercharging engine, as described above, the passage area of the valve member 054 increases linearly with respect to the opening degree of the valve member. Accordingly, upon controlling the relationship between the amount of the exhaust gas of the high-pressure-stage supercharger 1 and the amount of the exhaust gas bypassing the high-pressure-stage supercharger 1 and supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2, the amount of the exhaust gas supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 increases linearly with respect to the opening degree of the valve member. Subsequently, the rpm of the low-pressure-stage supercharger 2 increases, but the rpm of the high-pressure-stage supercharger 1 abruptly decreases.
For this reason, since the control range of the flow rate of the exhaust gas using a valve is narrow in low and medium rpm regions of the engine as shown by the line B of FIG. 3B, full-load torque of the engine is more reduced than that of the control shown in FIG. 3A. Additionally, since the two-stage supercharging region is smoothly changed to the one-stage supercharging region in a high rpm region by controlling the valve, the torque reduction is prevented.
Accordingly, since the passage area of the valve member 054 abruptly varies, it is difficult to smoothly carry out the selection operation to the one-stage supercharging operation of the low-pressure-stage supercharger 2 using the gentle variation of the passage area of the valve member 054. As a result, the exhaust gas amount control using the opening degree of the valve member 054 is difficult, and the power control range of the high-pressure-stage supercharger 1 and the low-pressure-stage supercharger 2 of the variable two-stage control region is narrowed.